use std::{cell::Cell, rc::Rc};

use cpal::{
    traits::{DeviceTrait, HostTrait, StreamTrait},
    Stream,
};
use wasm_bindgen::prelude::*;
use web_sys::console;

// This is like the `main` function, except for JavaScript.
#[wasm_bindgen(start)]
pub fn main_js() -> Result<(), JsValue> {
    // This provides better error messages in debug mode.
    // It's disabled in release mode, so it doesn't bloat up the file size.
    #[cfg(debug_assertions)]
    console_error_panic_hook::set_once();

    let document = gloo::utils::document();
    let play_button = document.get_element_by_id("play").unwrap();
    let stop_button = document.get_element_by_id("stop").unwrap();

    // stream needs to be referenced from the "play" and "stop" closures
    let stream = Rc::new(Cell::new(None));

    // set up play button
    {
        let stream = stream.clone();
        let closure = Closure::<dyn FnMut(_)>::new(move |_event: web_sys::MouseEvent| {
            stream.set(Some(beep()));
        });
        play_button
            .add_event_listener_with_callback("mousedown", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    // set up stop button
    {
        let closure = Closure::<dyn FnMut(_)>::new(move |_event: web_sys::MouseEvent| {
            // stop the stream by dropping it
            stream.take();
        });
        stop_button
            .add_event_listener_with_callback("mousedown", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    Ok(())
}

fn beep() -> Stream {
    let host = cpal::default_host();
    let device = host
        .default_output_device()
        .expect("failed to find a default output device");
    let config = device.default_output_config().unwrap();

    match config.sample_format() {
        cpal::SampleFormat::F32 => run::<f32>(&device, config.into()),
        cpal::SampleFormat::I16 => run::<i16>(&device, config.into()),
        cpal::SampleFormat::U16 => run::<u16>(&device, config.into()),
        _ => panic!("unsupported sample format"),
    }
}

fn run<T>(device: &cpal::Device, config: cpal::StreamConfig) -> Stream
where
    T: cpal::Sample + cpal::SizedSample + cpal::FromSample<f32>,
{
    let sample_rate = config.sample_rate as f32;
    let channels = config.channels as usize;

    // Produce a sinusoid of maximum amplitude.
    let mut sample_clock = 0f32;
    let mut next_value = move || {
        sample_clock = (sample_clock + 1.0) % sample_rate;
        (sample_clock * 440.0 * 2.0 * 3.141592 / sample_rate).sin()
    };

    let err_fn = |err| console::error_1(&format!("an error occurred on stream: {}", err).into());

    let stream = device
        .build_output_stream(
            config,
            move |data: &mut [T], _| write_data(data, channels, &mut next_value),
            err_fn,
            None,
        )
        .unwrap();
    stream.play().unwrap();
    stream
}

fn write_data<T>(output: &mut [T], channels: usize, next_sample: &mut dyn FnMut() -> f32)
where
    T: cpal::Sample + cpal::FromSample<f32>,
{
    for frame in output.chunks_mut(channels) {
        let sample = next_sample();
        let value = T::from_sample::<f32>(sample);
        for sample in frame.iter_mut() {
            *sample = value;
        }
    }
}